Vegetables like spinach, broccoli, cauliflower, etc. contain a chemical, I'm not sure what it's called, that tastes bitter. Some, like brussells sprouts, contain more than others, like spinach.
This chemical is not universally detected by taste buds. You need a genetic predisposition in order to taste the chemical. If you cannot taste it, you have no problem with the flavor or smell of those vegetables. If you can taste it, the smell and flavor are bitter and repulsive. The more sensitive you are, the worse it gets. I can eat raw spinach just fine, but cooked... *shudder* Broccoli, cauliflower, and brussels sprouts contain more of the chemical, and since I'm highly sensitive to it, I can be made to vomit at the mere smell of those vegetables being steamed, much less trying to eat them.
My childhood meals were full of horrible gagging and retching sounds until my mother remembered a science experiment she did in high school and put a drop of weak solution on my tongue to see if I was sensitive to the chemical. I was. The weakest concentration she had had me doubled over choking in the sink. She put the stronger ones away without testing them.
If I can figure out what the name of it is, you can probably pick up a weak solution of the stuff for testing, put a drop on your tongue, and see how sensitive to it you are.